1. Field of the Invention
The present invention relates to enhancing the safety of operation of aircraft and particularly to providing an aircraft crew with real-time information pertaining to wind conditions along an approach to and taking off from a runway. More specifically, this invention is directed to apparatus for detecting and providing an indication of wind gradient-wind shear conditions. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
The effects of wind gradients, and particularly passage through a wind shear zone, on aircraft have long been known. Recently, because of accidents attributed to wind shear, substantial attention has been devoted to developing the capability of warning aircraft crewmen of the existence of a shear line along the aircraft flight path. Much of this attention has been directed toward the utilization of known sensing devices, such as Doppler radar and acoustic radar, in wind shear warning systems. While radar technology appears ultimately to offer considerable promise, implementation of a wind shear warning system employing radar techniques will of necessity provide an expensive solution to the problem of providing the requisite warning. Further, the radar techniques presently under consideration for providing warning of the existence of wind shear zones lack the capability of providing the aircraft crew with real-time information concerning conditions along the aircraft flight path. Obviously, the aircraft operator needs information which informs him of the exact nature of the current wind conditions and further warns him when the wind conditions are such that extraordinary corrective measures are needed. Additionally, and most importantly, a wind shear warning system should provide the pilot with a "last chance" warning indicating that the instantaneous conditions are such that the maneuver being executed, for example a landing approach, should be terminated.
To further discuss wind shear warning systems in general, and it is to be noted that there is at present no apparatus available suitable for providing useful real-time information with respect to wind gradients or wind shear along an approach path to or departure path from a runway, such systems should preferably be possessed of a number of features and capabilities. Thus, a wind shear warning system must be able to detect a wind gradient, and particularly a discrete wind shear, on an approach path to a runway prior to the aircraft making a final approach to the runway. Similarly the system must be capable of measuring the magnitude of any detected wind gradient or shear along the approach path to the runway and providing information to the aircraft crew commensurate therewith prior to and at all points along the approach path. The warning system must also possess the capability of determining, prior to the approach, whether any existing wind gradient the aircraft will encounter is a decreasing headwind or tailwind or an increasing headwind or tailwind. Further, the system should provide the aircraft crew with information as to whether any shear zone detected has been traversed by the aircraft or still exists along the projected approach path of the aircraft. Also, prior to the aircraft's approach, the system must have the capability of determining and indicating whether a detected wind shear is a headwind/tailwind shear or a tailwind/headwind shear. The wind shear warning system should also include apparatus which will determine, taking into account the flight characteristics of the aircraft and the measured wind conditions which will be encountered, the "worst case" airspeed change which may be expected. Accordingly, the warning system should have the capability of calculating expected airspeed changes and continually updating the calculation in accordance with changes in the measured wind gradient or shear velocity differential and sensed actual aircraft speed. Some or all of the measured and calculated information should, of course, be displayed to the aircraft crew. Further, if the planned flight path of the aircraft calls for it to traverse a headwind/tailwind shear line, the system should compute the minimum altitude to which the aircraft may descend prior to passing the shear line and generate a readily perceivable abort warning signal should the approach path call for the aircraft to pass through the computed altitude prior to reaching the shear line. In the case of a tailwind/headwind shear line, the system must compute the airspeed which will exist after the shear is traversed and compare it to a preset maximum; an abort or go-around warning being automatically given if such preset maximum airspeed is exceeded at the flare altitude.
Further, the warning system should have the capability of detecting wind gradient-wind shear conditions which affect an aircraft's takeoff performance. These conditions are decreasing headwind gradients, increasing tailwind gradients, and headwind/tailwind shear zones encountered along the takeoff flight path. If the magnitude of the gradient or shear exceeds a precomputed level at a given altitude, taking into account the flight characteristics of the aircraft, the warning system should generate a "takeoff shear" warning to alert the flight crew that immediate action is necessary to maintain a safe airspeed.